The enteric nervous system (ENS) has 100 million neurons (more than the spinal cord). The surface area of the GI tract is larger than the surface area of the skin. There must be this tremendous amount of surface area in order to exchange the nutrients and wastes as food and water transit the GI tract.

The ENS operates without any input from the brain to control the movement and absorption of food across the wall of the intestines. However, the central nervous system (brain and spinal cord) does have the ability to control how fast food and water flow within the GI tract. There is a long nerve that extends from the brain called the Vagus that promotes digestion. It uses the neurotransmitter acetylcholine to communicate with the GI tract. The spinal cord interacts with the GI tract via the celiac and superior mesenteric ganglion to halt motility. It uses noradrelaline as its neurotransmitter. To avoid interfering with normal digestion, you should minimize medications with anti-cholinergic side-effects whenever possible – although 60% of medications have this side-effect to some degree. In addition, performing yoga or meditation can activate the Vagus nerve further improving digestion. Stress creates higher states of adrenaline as does consuming caffeinated beverages – both interfering with digestion. This can worsen conditions such as Irritable Bowel Syndrome.